How do I bring the cursor and X/Y intersection to the centre of the screen?
With shift + MiddleMouseButton you can drag the the x- and y-axis + the cursor to the center of your screen. Afterwards your circle and image will still be to the bottom left. Now you can re-center the image as you did before. To center the donout, rightclick on it, click on the + sign in the top right and set the location to x: 0, y:0, z:0